Magnesium base alloys

ABSTRACT

This invention provides magnesium base alloys having improved mechanical properties especially in the as cast state and consisting essentially, apart from impurities, of 6 to 12 percent by weight aluminum, from 0 to 3 percent by weight zinc, and at least 0.5 percent of each of silicon and manganese, the total content of silicon and manganese being 1.2 to 1.8 percent, and having a Mn/Si ratio of 0.6 to 1.5; balance magnesium.

ilnited States Patent Inventors Appl. No.

Priority Philip Andrew Fisher;

William Unsworth, both of Manchester, England June 24, 1969 Dec. 28, 1971 Magnesium Elektron Limited Swinton, Manchester, England June 26, 1968 Great Britain MAGNESIUM BASE ALLOYS 7 Claims, No Drawings US. Cl......

Int. (I

Field 01 Search [56] References Cited UNITED STATES PATENTS 1,959,913 5/1934 Gann et al. 75/168 1,946,069 2/1934 Grant 75/168 5 2,264,308 12/1941 l-lanawalt et a1. 75/ 168 2,264,310 12/1941 Hanawalt et a1. 75/168 3,240,593 3/1966 Schneider et al. 75/168 FOREIGN PATENTS 77,082 1955 Netherlands 75/ 168 Primary Examiner-Charles N. Lovell Attorney-Nolte and Nolte ABSTRACT: This invention provides magnesium base alloys having improved mechanical properties especially in the as cast state and consisting essentially, apart from impurities, of 6 balance magnesium.

MAGNESIUM BASE ALLOYS This invention relates to magnesium base alloys containing at least 80 percent magnesium.

The main object of the invention is to provide an alloy which has improved mechanical propertiesespecial1y proof stress, tensile stress and elongation of cast alloy at normal atmospheric temperatures and at elevated temperatures.

We have found that the mechanical properties of magnesium-aluminum alloys can be substantially increased by the addition of silicon and simultaneously increasing the manganese content.

We have found that improved mechanical properties can be obtained by incorporating at least 0.5 percent of each of silicon and manganese with a total content of manganese and silicon and manganese with a total content of manganese and silicon of 1.2 to 1.8 percent and a Mn/Si ratio of 0.6 to 1.5.

We have found that with a total content of manganese and silicon of 1.2 to 1.8 percent, the mechanical properties vary sharply and critically with the Mn/Si ratio with a peak at about 1.0. For example with an alloy containing 8 percent aluminum and 0.5 percent zinc, a graph of 0.2 percent proof stress shows a sharp peak between about 0.6 and 1.5 with the peak between 0.75 and 1.5.

Similarly a graph showing 0.2 proof stress with varying total manganese and silicon shows a depression from 0.1 to about 0.6 and thereafter an increase with a sharp rise above 0.6 with specially high values from 1.2 to 1.8 percent.

Moreover with a givensilicon content of over 0.5, e.g., 0.75 percent, a graph of increasing manganese content shows a drop from 0.1 to 0.2, a surprisingly sharp rise up to about 1.0 percent so that the upper part of the curve is represented by 0.55 to 1.4 percent and the top of the curve by 0.8 to 1.2 Mn.

The alloys are suitable for sand casting, gravity die casting and pressure die casting.

The improvement which can be achieved is illustrated by the following 0.2 percent proof stress values, expressed in tons per square inch, obtained on sand cast specimens at 180 C. for 16 hours.

It has been established that aging may be used to develop the properties, and is well known that the aging characteristics of magnesium-aluminum alloys are dependent, at least in part, one the aluminum content. Consequently, it is desirable to ensure that sufficient aluminum is present to give an aging response. However, with increasing aluminum contents ductility is reduced, and therefore the permissible range for aluminum is from 6 to 12 percent by weight, preferably 7 to 10 percent.

The presence of aluminum reduces the solubility of manganese in the liquid magnesium alloy, and if injurious manganese-rich particle clusters are to be minimized, it is necessary to control the manganese content within limits.

1n the alloy of the present invention there will normally be manganese-rich particles. It has heretofore been considered that such particles should be avoided in order to avoid machining difficulties but in practice we have found that machine operators have not reported any difficulty in machining alloys of the present invention.

Similarly, with the silicon content, this must also be controlled within limits to minimize segregation problems. It is preferred that Si and Mn are at least 0.5 percent each, e.g., at least 0.55 to 1.4 percent. Desirably Mn should be from 0.55 to 1.4 e.g., 0.8 to 1.2 percent. Also We prefer that manganese and silicon together should amount to at least 1.2 or even 1.3 percent, e.g., 1.5 to 1.8 percent. The ratio of Mn to Si may usefully be maintained in the range of 0.6 to 1.5 preferably 0.75 to 1.5. Zinc can be added to improve castability and is preferably 0.25 to 1.0 percent.

These alloys can be aged at temperatures within the range l00250 C. and preferably 200 C. The aging time will depend on the temperature and would range from 4 to 48 hours. A typical aging treatment would be 16 hours at C.

After aging the casting would be cooled in air, or alternatively quenched in water, oil or other suitable medium.

Alloys containing less than 6 percent aluminum are not suitable for the present invention as they do not provide the required value of proof stress and tensile strength.

The alloys of the present invention are best made by first preparing an alloy of Mg-Si-Al (and zinc if used) and finally adding the desired quantity of manganese, e.g., as manganous chloride. Alternatively an Al-Mn alloy can be used. The Si can be provided as an Al-Si alloy.

Alloys having particularly good mechanical properties had the following compositions:

Alloy A1% Mn% sm An% Mn/Si A s.s 0.76 0.85 0.54 0.0 88.1 0.91 0.88 0.61 1.03

The range of these alloys can be considered to be Am Mn% Si% 211% Mn/Si Mn Si (0 to [0 1O 10 alloys (alloys C and D) outside the scope of this invention were also tested of the following compositions viz, 9.% A1, 0.12% Mn, 0.94% Si, 0.54% Zn, 0.13 Mn/Si ratio, 8.7 A1, 0.5 Mn, 0.02 Si, 0.5 Zn, Mn/Si ratio 25.

Chill cast test bar properties at normal atmospheric temperatures were:

Elongation percent on 4 times Maximum tensile square root Alloy 0.2% proof stress stress of area A 7.3 tons/sq. inch 15.9 tons/sq.tnch 5 B 7.7 t0ns/sq.inel1.. 15.4 tons/sq.i nch 7 O-.. 5.5 tonslsq.lnch 13.1 tons/sq. mch 5 D 5.8 tons/sq. inch 16.4 tons/sq. inch 11 The alloy of the present invention can also be used for wrought products, e.g., rolled sheet, extrusions and forgings.

All percentages are by weight.

We claim:

1. A magnesium base alloy (containing) consisting essentially, apart from impurities, of 6 to 12 percent by weight aluminum, from 0 to 3 percent by weight zinc, and at least 0.5 percent of each of silicon and manganese, the total content of silicon and manganese being 1.2 to 1.8 percent and having a Mn/Si ratio of0.6 to 1.5; balance magnesium.

2. A magnesium base alloy as claimed in claim 1 having a Mn/Si ratio offrom 0.75 to 1.5.

3. A magnesium base alloy as claimed in claim 1 (or 2) wherein the manganese content is at least 0.55 percent 4. A magnesium base alloy as claimed in claim 1 (or 2) wherein the manganese content is 0.8 to 1.2 percent and silicon is 0.55 to 1.4 percent.

5. A magnesium base alloy as claimed in any of claims 1 to 4 containing 0.25 to 1.0 percent zinc.

6. A magnesium base alloy as claimed in claim 1 containing 7 to 9 percent aluminum, 0.6 to 1.2 percent manganese, 0.6 to 1.2 percent silicon, 0 to 3 percent zinc, and having a Mn/Si ratio of0.8 to 1.4.

7. A die-cast article of an alloy consisting essentially, apart from impurities, of 6 to 12 percent by weight aluminum, from 0 to 3 percent weight zinc, and at least 0.5 percent of each of silicon and manganese, the total content of silicon and manganese being 1.2 to 1.8 percent, and having a Mn/Si ratio of 0.6 to 1.5; balance magnesium. 

2. A magnesium base alloy as claimed in claim 1 having a Mn/Si ratio of from 0.75 to 1.5.
 3. A magnesium base alloy as claimed in claim 1 (or 2) wherein the manganese content is at least 0.55percent.
 4. A magnesium base alloy as claimed in claim 1 (or 2) wherein the manganese content is 0.8 to 1.2 percent and silicon is 0.55 to 1.4 percent.
 5. A magnesium base alloy as claimeD in any of claims 1 to 4 containing 0.25 to 1.0 percent zinc.
 6. A magnesium base alloy as claimed in claim 1 containing 7 to 9 percent aluminum, 0.6 to 1.2 percent manganese, 0.6 to 1.2 percent silicon, 0 to 3 percent zinc, and having a Mn/Si ratio of 0.8 to 1.4.
 7. A die-cast article of an alloy consisting essentially, apart from impurities, of 6 to 12 percent by weight aluminum, from 0 to 3 percent weight zinc, and at least 0.5 percent of each of silicon and manganese, the total content of silicon and manganese being 1.2 to 1.8 percent, and having a Mn/Si ratio of 0.6 to 1.5; balance magnesium. 